the catastrophic collapse of the Champlain Towers south in Miami is a timely reminder
to all structural engineers the responsibilities that they have when they undertake any structural
design the investigation into this catastrophic failure is also something that all structural
engineers should take note of to ensure that their designs will not have the same fatal design flaw
so that we learn from this catastrophic event so what do we know so far about the Champlain
Towers in Miami well we know that it was built as a twin tower so we got the south
and the north Champlain Towers it was the south one that actually collapsed
and we know that roughly half the building was involved in the catastrophic failure
the location of the tower also points to key areas that we should be looking at
to see whether they are some of the causes of the structural failure you see it's located on the
sea so it has nice salty sea breezes blowing over the building this can cause detrimental effects on
the substructure of the building as salty breezes blow and impregnate into this concrete potentially
damaging the structural reinforcement hidden within so this can cause damage over time that
slowly degrades single elements this degradation is more commonly known as concrete cancer as the
chemical reactions start to occur and the steel starts to rust the structure is slowly degraded
from the inside out essentially hidden from site as concrete cancer starts to progress
when you look at the structure underneath you may see signs of rust forming on the underside
of slabs or on the outside of columns indication that the steel underneath is potentially rusting
and as it progresses further and further the rust starts to apply additional pressures on the
concrete as it starts to expand to the point where it fails the tensile capacity of the concrete
causing spalling of the concrete and exposing the steel reinforcement underneath
this spawling typically occurs later in the piece so signs of spoiling
must indicate that the structure needs to be looked at further so there is additional
maintenance work that needs to happen to stop the rusting from occurring and assessments to ensure
that the structure has not been degraded to the point that it requires additional rectification to
repair the issue i know this is a sobering video but don't forget to hit that like button what this
does it encourages me to keep making content like this and to get it out to more engineers
there was also reports in the 1990s that this building was slowly settling into the ground of
roughly one to two mils could this be indications of footings or substructures having some issue
that needed to be resolved definitely an area that the investigations will need to focus on to see
whether it either exacerbated or potentially led up to the causes of the damage in the structure
there was reports of complaints from residents about vibrations felt in the structure
from construction activities occurring from an adjacent building now this is not uncommon that
vibrations are felt in the structure from major activities such as construction as the soil
is not a solid material will propagate vibrations into your building however is
this indicative of potential damage that occurred from that construction activities from having
too much allowances on those vibrations or potential problems in the structure prior to this
catastrophic collapse again another question that needs to be asked in these in future investigations
we do know at the time of the collapse there was construction and works being done
on the roof of Champlain Towers when most people think about construction works they
think about the additional weight of machinery or equipment or materials that may be placed up there
where the weight of materials will not be sufficient enough to cause a catastrophic failure
like we saw as we have all these additional flaws where the load can be distributed from
the additional weight of some construction work on the top of the tower would be so insignificant
compared to the overall weight of the structure however construction work does apply additional
forces on the building such as vibrations so if vibrations were to propagate through the structure
in combination with the concrete cancer that we discussed earlier
it may have caused additional degradation to some of the supporting structures
as that tensile capacity on the concrete cancer was pushing the concrete off the vibrations may
have just been enough to fail the tensile capacity of the concrete causing additional spalling
and damaging some of the critical elements in the structure this is something that the investigation
will need to have a look at to see whether the concrete cancer was actually in the structure
and whether it was exacerbated by the repair works being done on the roof
it was also known that there was damage being done on the pool deck through leaking of the
waterproofing membrane and cracking in the substructure this potentially leads to leaking
of chlorine water into the structure which will be highly corrosive and damaging to the structure and
potentially also leaking into the footing systems causing additional settlement in the structure
that may have exacerbated this issue so was the failure mechanisms that we were seeing in the pool
deck indicative of a future failure i'm sure this will be answered in the future reports that come
out in the years and months ahead we also have public access to some of the reports that written
about some of the damage that was observed on Champlain Towers prior to its collapse
and some recommended repair works were also in those reports as we look through these reports
we can see many photos that are showing big signs of concrete cancer and spalling in the structure
and we can also see exposed reinforcement in some of these pictures the report also indicates
that there was also additional cracks forming off previous repair works that had occurred earlier as
the report states that where they had previously epoxy ejected the cracks there was additional
cracks propagating off this location so this is indicative that there were potential stresses in
there either from thermal contraction or expansion or from some other element in the structure
that require the structure to crack in that location and by just injecting the
cracks you will not fix the underlying issue and that stress still needs to be relieved
before we start to analyze the footage that may point to some areas where the investigations need
to look into it's important that you understand the term disproportionate collapse so what is
disproportionate collapse disproportionate collapse is a term that structural engineers
used to define a failure mechanism so when you have a localized area receiving damage
a disproportionate amount of the building is not to collapse from that single failure
for example, if you may lose a column you do not lose the whole building
and disproportionate collapse is not just one mechanism and it's come about from the 1970s with
a failure at Ronan point now this was a building in the UK that had a series of walls stacked
on top of each other what happened is you had a a small gas explosion on one of the bottom floors
that blew out one of the walls and the way the building was designed and detailed it came down
like a house of cards collapsing all the other floors above it so what the royal commission found
from this was there's minimum tire reinforcement that you need between floors to make sure that
if you do have a failure down lower the building is able to act in somewhat of a continuing
reaction and hold itself up allowing residents to leave another critical example from recent
times is the new Orleans Hard Rock Cafe collapse if we're looking at the footage we can see that
the floors are pancaking on top of each other so when one floor came down on the floor above it
overloads that floor bringing the next floor down and the next floor down creating a cascade effect
the building collapsing from top-down for this type of failure the building needs to be designed
such that the floor below it is able to support the floor above it if it lands on top of it
under service conditions and we're not talking about ultimate cases, it just needs to not collapse
and this is quite commonly the case when you're looking at the design of buildings they generally have
back propping going up and so the floor below it needs to support some wet weight of the concrete
above which is the primary component of the load in the structure or the other example is if we
lose a load-bearing element whether it be a wall or a column so we lose that column now the floors
will drop we detail the slabs in such a way that you've got continuous reinforcement or continuous
post tensioning allowing the slabs to go into catenary so what this means is that firstly you
overload those first set of columns adjacent to it now those columns have additional load-bearing
capacity as they've been factored up both in their loading components and they've had a reduction
in material safety factors so those columns under a service, condition have enough capacity
to support additional loads if you lose a single element and then you have the container reactions
and this is from having continuous reinforcement in the slab both in the top and the bottom so if
it does drop down it may sag a long way or if you have got post-tensioning which is normally
those continuous tendons that are really good for these catenary forces that may occur and these
structures they do not need to last for days weeks or months they only need to stand up for hours
that allow people to evacuate their residence so you should not see such failures as what we saw in
the Miami condo where we had this catastrophic failure of those floors dropping causing the
whole building to pancake on top of each other there was CCTV footage from an adjacent building
showing the collapse and where the investigation should start to look for the potential mechanism
of this failure when watching this footage you'll see that the building failed in essentially three
areas in the first you can see the front facade drop of the tower then the remaining
structure behind it comes down then finally the third component which is the seaside core
is the final element of the structure to fail so let's step into this footage so we can see
the front facade has dropped meanwhile the back half of the building is still remaining in place
and it's actually gone a fair way down before the back half of the building
also starts to come down so potentially that first half the building was the first failure mechanism
and as it came down it caused additional damage to this number two element in behind it now as
we can see the number two element starts to come down wherever that third part of the structure
is still remaining until the remaining parts of the structure is almost on the ground is when
this final element of the tower comes over again potentially indicating that there may have been
damage from the first two components collapsing that caused that final section of the building
to come down as was seen in that footage the failure occurred firstly in that first section
and was sudden and catastrophic this points to a number of failure mechanisms either a shear
failure on a transfer deck or more than likely one of the compression members such as a wall
or columns had a failure that caused the whole tower to come down as we know from the reports
there were no major signs of distress other than the concrete spalling but it was not indicative
of a flexure failure that would see major cracking in the structure before it actually occurs
where if we had a failure in such an element as a column we may not know it's failed until it's too
late so there are essentially three questions that need to be asked into this failure what was the
cause of this failure was there any ways that we could have prevented this catastrophic collapse
and was the collapse disproportionate to the damage that the building had if you
have any ideas or knowledge of the actual causes of failure at Miami please comment
below and if you're interested in structural engineering don't forget to hit the subscribe
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